So the latest update on this
I decided to try and look at Thomas Snrs other children
Jessie b.1827 appears to have died very young, prior to the departure to Ferry Port.
Jane b1833 married James Spink in 1851, in Montrose. James Spink was a Merchant Seaman.
David b.1836 became a hairdresser. In 1861 he was still living with his mother Charlotte and later married Ann Logan(s) in 1868, in Montrose. He died in Montrose in 1902 and on his DC it states that his parents were Thomas Nicol (Fisherman) and Charlotte Gardyne.
Charlotte Jnr b.1838, finding it difficult to pin her down at moment.
So interesting, but unfortunately does not get me any closer in identifying who Thomas Snr actually was.
The Thomas Nicol born at St Vigeans in 1794, is a candidate and I was unable to locate him in the 1841 census. Clealry the evidence I have is that Thomas Snr most likely died between 1838 and 1841.